Why iPhone Status Bars Are Showing Unexpected Ads – The PLMN & NITZ Explanation

The status bar at the top of a mobile screen normally shows the network operator, signal strength, Wi‑Fi status, battery level, and sometimes a VIP tag for high‑cost plans.

Recently, many China Mobile users have posted screenshots showing that the carrier name in the status bar has been replaced by various advertising messages, which differ by region and often contain local slogans or promotions.

Examples include campus greetings like "Hello new student" for university cards, regional ads for Jiangsu, Shandong, Henan, and other provinces, and promotions for events such as the Qingdao Beer Festival.

These ads appear mainly on iPhone devices, with occasional reports from Android users.

To understand why, we need to look at how the carrier name is displayed. The process starts with the PLMN (Public Land Mobile Network) identifier, which consists of a Mobile Country Code (MCC) and a Mobile Network Code (MNC). The PLMN name—e.g., "China Mobile"—can be sourced from three places:

SPN stored on the USIM card

PLMN name broadcast by the base station via the NITZ protocol

Name stored locally on the device from the last network connection

The priority order is USIM SPN > NITZ broadcast > device‑stored name.

According to the 3GPP standards, the operator name should be shown as defined by the network. However, China Mobile’s 2024 5G Phone Product White Paper now requires manufacturers to support custom logos and to display NITZ messages in place of the original carrier label, with a rollout schedule that mandates this feature for all new devices from July 1 2024 and for all devices entering the market in 2025.

China Broadcasting’s white paper states that if the core network does not send an NITZ message, the default "China Broadcasting" name is shown; otherwise, the NITZ message must replace the carrier label.

These requirements have sparked debate because they may violate 3GPP rules on operator name display, and users find the unclosable ads intrusive. While Android users can change the carrier name in settings, iPhone users would need to jailbreak and install plugins to modify the status bar, which is not feasible for most.

Furthermore, the NITZ message length is limited to 50 bytes and may scroll, adding to the annoyance. Nonetheless, carriers argue that such messages could be useful for notifying users about low balance or data limits.